Unless otherwise indicated herein, the description provided in this section is not itself prior art to the claims and is not admitted to be prior art by inclusion in this section.
To provide cellular wireless communication service, a wireless service provider typically operates a radio access network (RAN) that includes at least one base station (BS) that radiates to define wireless coverage areas, such as cells and cell sectors, in which wireless communication devices (WCDs), such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly-equipped communication devices, can operate. In turn, each BS may be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a WCD within coverage of the RAN may engage in air interface communication with a BS and may thereby communicate via the BS with various remote network entities or with other WCDs served by the BS.
In general, a RAN may operate in accordance with a particular air interface protocol or “radio access technology,” that includes a downlink (also known as a forward link) and an uplink (also known as a reverse link). The downlink is the communication from the BS to the WCD and the uplink is the communication from the WCD to the BS. Examples of existing air interface protocols include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) or Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), and Global System for Mobile Communications (GSM), among others. Each protocol may define its own procedures for registration of WCDs, initiation of communications, handoff between coverage areas, and functions related to air interface communication.
In accordance with the air interface protocol, each coverage area may operate on one or more carriers in particular frequency bands (such as 698-960 MHz, 1610-2025 MHz, etc.), with each carrier defining one or more frequency channels for carrying information between the BS and WCDs. By way of example, each carrier may define a downlink frequency channel and a separate uplink frequency channel, each spanning a particular bandwidth in the frequency spectrum. Or each carrier may define a single frequency channel that is divided over time into downlink and uplink segments.
In addition, each coverage area may define various logical channels for carrying certain types of information, data, or signaling between the BS and WCDs, with the channels being defined in various ways, such as through frequency division multiplexing, time division multiplexing, and/or code division multiplexing, for instance. By way of example, each coverage area may define a pilot channel or reference channel for carrying a pilot signal or reference signal that WCDs may detect as an indication of coverage and may measure to evaluate coverage strength. Further, each coverage area may define one or more downlink control channels or other resources on which the BS may transmit control messages or other information to WCDs, and one or more uplink control channels or other resources on which WCDs may transmit control messages to the BS. Further, each coverage area may define one or more traffic channels or other resources for carrying bearer data (e.g., application layer traffic), such as voice communication, video communication, web communication, gaming communication, Session Initiation Protocol (SIP) signaling, and other data between the BS and WCDs.
When a WCD first powers on or enters into a BS's coverage area, the WCD may register with the RAN in that coverage area by transmitting a registration request, such as an attach request, to the BS serving that coverage area. In response to the BS receiving the registration request, the BS or associated network infrastructure may authenticate and authorize the WCD for service and may reserve network resources for use to serve the WCD. For instance, the registration request may lead to setup in the network of one or more logical bearers, data-link-layer connections, or the like, as well as assignment to the WCD of a radio-link-layer connection defining a downlink and uplink over the air between the WCD and the BS.
Once the WCD is registered with the BS, the WCD may then operate in either a connected mode or an idle mode. In the connected mode, the WCD may engage in communication of bearer data, such as by transmitting bearer data on uplink traffic channels to the BS and receiving bearer data on downlink traffic channels from the BS. And in the idle mode, the WCD may monitor a downlink control channel for an indication from the RAN that the WCD should begin a communication session.